Power from the sun and the wind

Feb 29, 2008

To the editor: If solar photovoltaic output per square foot of panel area hadn’t doubled in the past five years, a comparison of the two popular cruising boat technologies wouldn’t be worthwhile. We have a five year-old 54” x 29.5”, 11-square foot, 64-watt Uni-Solar adjustable panel mounted on the top of the dodger and a post-mounted, 400-watt Air-X Marine wind generator on the aft deck.

After living with both solar and wind power on anchor and on moorings we are considering replacing the 64-watt panel with a new 130-watt solar panel because it is about the same size (10 square feet) as the existing panel. Like many modern voyagers we have managed to squeeze a full complement of electric and electronic equipment aboard our vintage 34-foot Tartan sloop. We use an average of 110 amp-hours of electric energy per day. When it’s hotter than 95° F the 12-volt refrigerator operates longer, and our daily use increases to about 125 amp-hours. We know about our daily usage because we installed a Link 10 battery monitor last year along with 330 amp-hours of new Trojan house batteries. We only operate our Honda 2000 generator to top-off our batteries when we’ve gained as much energy as possible from sun and wind.The question is do we keep the wind generator if we double the wattage of the solar panel?

Living with our solar panelWe’ve learned a couple of things about our existing solar panel. First, it’s important to have the panel adjustable to the angle of the sun: the daily output is doubled as the panel is orientated as close to 90° to the sun as possible. It’s hard to note the difference in solar panel output having more than four panel adjustments including laying the panel flat on the dodger when the sun is nearly overhead. When we’re on board, solar panel adjustment has become part of our daily routine. When we’re ashore we set the panel at a modest angle, either fore or aft depending on which way the boat is pointing, knowing the sun will move overhead while we’re off the boat.

We’ve noticed on our Link 10 battery monitor our 64-watt panel produces a maximum of 4.2 amps at about 13 volts during the middle of the day when the panel is flat on the dodger. Even being diligent about changing the orientation of the panel, it’s difficult to get more than one to two amps when the sun first appears in the morning and when it’s beginning to set. During a normal sunny winter day in southern waters the solar panel contributes between 27 to 30 amp-hours to the house batteries.

Our Uni-Solar 64-watt panel cost about $300 five years ago (not including the simple, inexpensive, panel adjustment mechanism on top of the dodger). This computes to $4.69/watt. Of course, it costs nothing to operate a solar panel and so far, no maintenance required except for annually cleaning the pins in the on-deck connector. Given the cost of the panel and the fact that it produces 27 to 30 amp-hours per day, it’s likely much more cost-effective to run our $850 Honda 2000 generator for an hour at 35 to 50 amps to charge house batteries, all the while using less than $1.50 worth of gasoline. We are cruising conservationists and try to use as little fossil energy as possible and diligently adjust our solar panel before we walk to the market.

We’re now considering a new 130-watt Kyocera solar panel that will fit on top of the dodger and can easily be made to work with the existing adjustment mechanism. The new Kyocera panel costs $600 (retail) that computes to $4.60/watt, interestingly about the same as the cost per watt 5 years ago. We’re expecting the new panel to produce a maximum of seven to eight amps or 50 amp-hours each day, about half our daily amp-hour requirements. Now our Honda 2000 should run about one-third less time. We hope to sell the 64-watt Uni-Solar panel and defray some of the cost of the new one.

Living with our wind generatorWe have lived with our Air-X Marine 400-watt wind generator for four years. It does the job and is reliable but it needs at least 13 knots of wind to generate a meaningful amount of electric current. We get a little more than two amps at 13 knots and 20 amps at 25-plus knots of wind. (Solar photovoltaic panel output is linear whereas the wind generation amp output is non-linear.)

It’s hard to measure the daily contribution to charging house batteries given that the wind is up and down and blows less than 13 knots most of the time. To be sure, at 25 knots the wind generator provides 20 amps (or more) of charging current but the harder the wind blows the noisier it gets: when the wind blows 20 to 25 knots while we’re trying to sleep at night we frequently shut down the wind generator. When the wind blows a steady 15 knots all day, the wind generator does a good job and occasionally tops-off the batteries. However, steady 15 knots of wind over a 24-hour period happens only a couple of weeks during a six-month winter cruise.

It’s clear our wind generator is much less cost effective than our solar panel and our Honda 2000 generator. Wind energy is free, of course, but the initial cost of the wind generator is more than the Honda and provides much less energy over a winter period even assuming $1/day gasoline cost. Unfortunately, advancements in wind generation technology usable on cruising boats haven’t kept pace with advancements in photovoltaic panels or compact gasoline generators.

We have other problems with the wind generator besides the uncertain charging current: when underway, the generator has an effect on our sailing performance unless it’s shut down. And even then it creates noticeable wind resistance; it sticks up nine feet and can be a hazard when rotating in winds more than 20 knots (we’ve killed at least one seagull). I think it’s ugly; Kathy likes it! Yes, aesthetics count: we never forget it’s a sailboat and we do like to sail. On the other hand the solar panel is out of sight on the dodger.

Being an electrical engineer I probably examine our on board energy systems more than most voyagers and likely bore our friends. Our plan is to double the size of the solar panel and remove the wind generator. I’ve concluded that a 130-watt solar panel will reliably provide much more energy over a six-month cruise than the 400-watt wind generator. My advice is that cruisers seriously consider the new generation of high-output solar panels and devote as much space as possible. It’s even better if they can be mechanically orientated toward the sun. On top of the bimini seems to be a popular location.

— Richard de Grasse holds a USCG Masters license, is a Commodore in the Seven Seas Cruising Association and a member of the Ocean Cruising Club. He and his first mate Kathy live in Islesboro, Maine, when not voyaging.